The solution to this problem is to repair the distribution cover. If it is uneven, it will need to be smoothed out. Also, consider correcting surface drainage around your property if. A septic distribution box (D-box) is a concrete or plastic junction that evenly distributes wastewater from your septic tank to all drainfield lateral lines. Clogging. When your distribution box shows leakage signs, you have your first clue which tells you that you drainage system beyond the D-Box is not functioning properly.